Sierra Leone's head doctor in fighting the current outbreak of the Ebola virus, the deadliest in history, has himself contracted the disease. Sheik Umar Khan, who has treated more than 100 Ebola victims, has been hailed as a "national hero" by the health ministry.

The 39-year-old doctor has been transferred to a treatment ward run by humanitarian group Doctors Without Borders, Reuters reported on Wednesday. Another three nurses in the same treatment clinic have reportedly died after contracting the disease.

The outbreak has killed 206 people alone in Sierra Leone since it began in February, and over 600 in total, including deaths in Guinea and Liberia.

Khan had been aware of the dangers of working near Ebola patients, and back in June admitted that he was afraid for his life.

"Health workers are prone to the disease because we are the first port of call for somebody who is sickened by disease. Even with the full protective clothing you put on, you are at risk," the doctor told Reuters in another interview.

Sierra Leone Health Minister Miatta Kargbo branded Khan a "national hero" and said that she would "do anything and everything in my power to ensure he survives."

The World Health Organization, which has been providing updates on the spread of the disease, has warned that close to 90 percent of patients who contract Ebola die from the disease, though the rate has gone down with better treatment.

The latest update from Saturday noted that there have been 1048 cases of Ebola virus across West Africa since the outbreak began, and so far there have been 632 reported deaths.

Several humanitarian groups are working in the region, including Christian relief group Samaritan's Purse, which is directing efforts at an Ebola isolation center in Liberia, near the border with Guinea.

"This is the largest outbreak of Ebola since it was first discovered in 1976 and it is the largest outbreak in Western Africa, with cases now showing up in national capital cities," said Ken Isaacs, vice president of programs and government relations for Samaritan's Purse. "Along with medical treatment, awareness and education are the keys to containing this outbreak."

In an update on Tuesday, the group called on the Christian community to continue praying for the staff that is battling the outbreak, and shared the testimonies of some of the patients who have been cured at the Liberia facility.

Symptoms of the deadly disease include diarrhea, vomiting and internal and external bleeding, WHO says.